The present invention relates to the novel benzylidene compounds, an ultraviolet-absorbing cosmetic composition and an ultraviolet absorber. More particularly, the invention relates to benzylidene compounds represented by the formula (I): ##STR5## wherein A is a group represented by the formula (II): ##STR6## or the formula (III): ##STR7## wherein B represents hydrogen atom or an acetyl group; W represents hydrogen atom or --CH.sub.2 --CH.sub.2 --CO--O--R; X.sup.1, X.sup.2 and X.sup.3 represent independently hydrogen atom, a hydroxyl group or a methoxyl group (two or three of X.sup.1, X.sup.2 and X.sup.3 may be the same or all of them may be different); Y represents oxygen atom or an imino group (--NH--); Z represents a methyl group or a phenyl group; and R represents a straight chain alkyl group having 1 to 18 carbon atoms, or branched or cyclic alkyl group having 3 to 18 carbon atoms, provided that when A is a group represented by the formula (II), R is not an alkyl group having 1 to 2 carbon atoms, and when A is a group represented by the formula (III) and X.sup.1, X.sup.2 and X.sup.3 are hydrogen atom, R is not an alkyl group having 1 to 2 carbon atoms, an ultraviolet-absorbing cosmetic composition containing at least one of the benzylidene compounds represented by the formula (I), and an ultraviolet absorber comprising at least one of the benzylidene compounds represented by the formula (I).
In the field of cosmetics, use of ultraviolet absorbers has been noted from long ago for preventing the harmful effect of ultraviolet rays to the skin and a number of ultraviolet absorbers for use in cosmetics have been developed.
It is known that ultraviolet rays, when the skin has been exposed thereto, cause various changes in the skin tissue. In the dermatology, ultraviolet rays are classified into long-wavelength ultraviolet rays (400-320 nm), medium-wavelength ultraviolet rays (320-290 nm) and short-wavelength ultraviolet rays (290-100 nm), and they are referred to as UV-A, UV-B and UV-C, respectively.
Among them, UV-C is absorbed in the ozone layer and scarcely reaches the surface of the earth. As for UV-B, it is known that when the skin is exposed to UV-B at a dose of more than a certain level, UV-B causes erythema or blisters on the skin or causes pigmentation in the skin. On the other hand, UV-A has been said to exert no much influence on the skin. However, as a result of examinations by electron microscopes and histological investigations, it was found recently that UV-A does cause a change in elastic fibers in vascular walls or connective tissues. Further, UV-A gives a damage to the hypersensitive skin or the skin exposed to the sunlight for a long time. It has been also reported that UV-A promotes the action of UV-B (J. Willis, A. Kligman and J. Epstein: "Photo-enhancement", The Journal of Investigative Dermatology, Vol. 59, No. 6, p. 416, 1973). Thus, screening the skin from UV-A is as important as that from UV-B.
As UV-B absorbers, there are used benzophenones absorbers, salicylic acids absorbers, cinnamic acids absorbers, para-aminobenzoic acids absorbers, etc. Among such known ultraviolet absorbers, however, there are few which are satisfactory in effect, safety, solubility, stability and other properties.
The history of study on UV-A is not long, and materials which, when applied to the skin, can effectively absorb UV-A are scarcely known. Only such materials known are dibenzoylmethane derivatives, cinnamic acid derivatives and chalcone derivatives [West German Patent Application Laid-Open Nos. 2,278,241 and 2,728,243, and Japanese Patent Application Laid-Open (KOKAI) Nos. 51-61641('76), 52-46056('77), 57-59840('82), 57-197209('82) and 60-109544('85)].
For instance, Japanese Patent Application Laid-Open (KOKAI) No. 51-61641('76) discloses a light screening agent containing a compound of the formula: ##STR8## (wherein R is an alkyl group having 1 to 3 carbon atoms) with a miscible cosmetic base, and Japanese Patent Application Laid-Open (KOKAI) No. 52-46056('77) discloses an ultraviolet absorber containing at least one of the compounds represented by the formula: ##STR9## (wherein R and R.sup.1 represent a straight chain or branched alkyl group having 1 to 8 carbon atoms, n is an integer of 0 to 3, and n' is an integer of 1 to 3). Japanese Patent Application Laid-Open (KOKAI) No. 57-59840('82) discloses a composition having the properties for protecting the skin from ultraviolet radiation, which comprises at least one of the dibenzoylmethane derivatives represented by the formula: ##STR10## (wherein R.sup.1 and R.sup.2 represent a lower alkyl group or a hydroxyalkyl group, R.sup.3 represents a lower alkyl group or an alkoxyl group, n is an integer of 0 to 3, and X.sup..crclbar. represents anion derived from a mineral acid or an organic acid) and a cosmetically acceptable carrier. Japanese Patent Application Laid-Open (KOKAI) No. 57-197209('82) discloses a composition comprising as a light screening agent at least one of the hydroxyl derivatives of dibenzoylmethanes of the formula: ##STR11## (wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 represent hydrogen atom, a halogen atom, a straight chain or branched alkyl group having 1 to 12 carbon atoms, or an alkoxyl group having 1 to 4 carbon atoms, and R represents hydrogen atom or an alkyl group having 1 to 4 carbon atoms) and a cosmetically acceptable carrier. Also, Japanese Patent Application Laid-Open (KOKAI) No. 60-109544('85) discloses an ultraviolet absorber containing as an active ingredient a chalcone derivative represented by the formula: ##STR12## (wherein R.sup.1 represents hydrogen atom or a methyl group, and R.sup.2 represents a straight chain or branched aliphatic hydrocarbon group having 2 to 24 carbon atoms).
Besides the above-mentioned ultraviolet absorbers, there are also used the inorganic powders having the function to physically reflect or scatter the ultraviolet rays, such as titanium dioxide, zinc oxide, iron oxide, etc.
The benzophenones ultraviolet absorbers have an activity of absorbing long-wavelength ultraviolet rays (320-400 nm) but are low in absorptivity of medium-wavelength ultraviolet rays (290-320 nm) which are considered to cause blistering, etc., of the skin.
The para-aminobenzoic acids and cinnamic acids ultraviolet absorbers are high in UV absorbing effect, but it is said that they have the problem in stability. The salicylic acids UV absorbers are low in UV absorbing effect, so that no satisfactory effect can be expected unless they are blended in a large amount.
The inorganic powders are limited in their use to certain cosmetics types in which they can be compounded, and they also have the problem that they might be colored when compounded in a large quantity.
Ultraviolet absorbers are also used as an additive for preventing deterioration of resins. As an additive, salicylic acids UV absorbers, benzophenones UV absorbers, triazoles UV absorbers and cyanoacrylates UV absorbers are exemplified. However, the salicylic acids and benzophenones UV absorbers are low in absorptivity of ultraviolet rays of wavelength of around 300-320 nm which are said to give influences to resins such as polyethylene, polypropylene and polyvinyl chloride, while the triazoles UV absorbers are said to have the problem in safety and sanitation.
As described above, although various ultraviolet absorbers have been developed, there is yet available no ultraviolet absorber which can meet all of the requirements for UV absorptivity, safety, solubility in solvents and resins, and stability. Thus, the realization of an ultraviolet absorber having excellent UV absorptivity, safety and stability and a cosmetic composition containing such UV absorber has been desired.
In view of the above, as a result of more extensive studies, it has been found that the benzylidene compounds represented by the general formula (I) have a high absorptivity of ultraviolet rays of medium wavelength (240-400 nm) and are also easily soluble in various kinds of animal oils, vegetable oils, fats and oils, and organic solvents, and that the cosmetic compositions containing at least one of such compounds are possessed of good UV absorptivity, effective for preventing erythema, etc., of the skin, stable to light and heat, and also not stimulant nor injurious to the skin, lips, hair, nails, etc. The present invention has been attained on the basis of such finding.